A system is disclosed in German Disclosure document OS No. 28 11 574.7 in which an externally controlled input signal signifies the desired power output of an internal combustion engine. A value e.g. the amplitude of this signal is used to address a memory or storage device storing a characteristic curve of the internal combustion engine. Specifically, for each value of desired power, the required fuel supply value specified by the characteristic curve is generated. The required fuel supply value, in the form of a corresponding signal, is then used to control the throttle valve of a carburetor or the control rod in an injection pump of a diesel motor. This required fuel supply value, i.e. the characteristic curve, is designed for the value which will optimize fuel consumption of the engine at the given desired power. Further, the desired power signal is also applied to a storage storing the transmission characteristic. A signal corresponding to the output speed of the engine is also applied to the transmission characteristic storage. The latter furnishes a signal controlling the transmission ratio in response to the two signals applied thereto. This system can be used both with transmissions in which the gear ratio is controlled in steps and transmissions wherein a continuous adjustment of the gear ratio is possible. In this known system, a switch is provided which switches it from a minimum consumption regulation to a regulation optimizing the power output when the required fuel signal and the speed of the engine signify an actual power output substantially less than the desired power output, i.e. when a large increase in power output is required. This apparatus requires two storages for characteristic curves in addition to the above-mentioned switch which must be present to allow rapid increases in power output when required.
In the system described in U.S. Pat. No. 3,324,740, the driver regulates the transmission ratio and the engine speed under normal operating conditions, the engine speed being controlled in conventional fashion by control of the fuel supply via the carburetor or the injection pump. A first regulator controls the desired engine speed by adjusting the throttle valve, while a second regulator controls the transmission ratio. A third regulator is provided to prevent stalling of the engine by changing the transmission ratio if the output shaft is overloaded. This regulator also prevents the speed of the engine from exceeding a predetermined maximum speed. However, this third regulator only becomes effectve when the desired engine speed cannot be maintained by the first regulator. A system for controlling the fuel consumption in an engine driving a hydrostatic transmission having a continuously variable transmission ratio is disclosed in U.S. Pat. No. 3,927,528. In this system, the driving motor, an internal combustion engine and the hydrostatic transmission are controlled in response to the desired torque signified by the position of the gas pedal and the actual torque derived from the hydrostatic transmission pressure and volume. An engine speed sensor senses the output speed of the engine and furnishes an engine speed signal corresponding thereto. The engine speed signal is used to shift the null point of a regulating stage which is responsive to a signal signifying the then-present engine torque and controls the position of a tapered disk fixing the transmission ratio of the hydrostatic transmission.
It is a disadvantage of both of the above-described systems that the operating parameters of the engine which are required to effect minimum fuel consumption and therefore the cleanest possible exhaust are either not utilized or are only approximated. The goal of minimum fuel consumption and clean exhaust is therefore not achieved.
In U.S. Pat. No. 3,890,360, a system is described in which the control for fuel supply and for the transmission ratio is achieved by first comparing the signal resulting from operation of the foot pedal (which signifies a desired engine speed signal) to a signal signifying the actual engine speed and utilizing the difference to control solenoid valves which control the continuously variable transmission ratio. The difference signal is also used to control a solenoid valve which regulates the throttle valve of position. In this system, too, optimum fuel consumption is not really achieved, since all operating parameters relevant thereto are not fully considered. In addition, none of the above-described systems allow the full power output of the engine to be available when needed under emergency conditions. For example, if the driver is trying to pass another vehicle on the road, full power should be available immediately.